Cal-stat Application Basics


Cal-stat temperature controls are often a primary component of a heated system or product. Proper application of the Cal-stat control is a key requirement to optimize system performance and efficiency. System design determines the accuracy of temperature control to a much greater extent then the accuracy of the Cal-stat controls themselves. The following should be kept in mind when designing a heated product or system:

1. All parts of the system should be insulated where feasible to reduce heat losses.
2. Temperature gradients (differences in temperature from one part of the system to another) must exist to allow heat transfer, however, the presence of extreme or rapidly changing temperature gradients make close control very difficult.
3. In most applications the system should be as compact as possible.
4. Consider the use of more than one Cal-stat in larger systems with more than one heater.
5. Position of the Cal-stat temperature control should be considered to balance the response to temperature change in the controlled material including placement of the Cal-stat control at a location indicative of the average temperature of the systems. Placement of the Cal-stat at a location too close to the heater or heat source will result in the Cal-stat sensing the temperature of the heater and not the media being heated, typically resulting in lower media temperature and erratic control Placement of the Cal-stat in an area of the material being heated that is not indicative of the average temperature may result in too high a temperature, too low a temperature, and/or erratic control.
6. Cal-stats used with cartridge heaters in a platen or die should be located no closer than 1/2" to the heater(s) or in the middle between guidelines.
7. Cal-stats without mounting fittings are designed for temperature control applications with direct insertion into solids. Models with mounting fittings can also be applied into liquids and gases.
8. Cal-stats are recommended for resistance loads and not for inductive loads.
9. Use of magnetic contactors or relays in conjunction with the Cal-stats are not recommended since the slow make and break switching may cause contact chatter and arcing of both the Cal-stat and contactor switch contacts.
10. Due to their sensitivity, Cal-stats are not recommended in applications where extreme vibration exists. The affects of vibration are minimized if the if the Cal-stat installed with the vibration parallel to the shell tube.